Update guide on RestComm XMS configuration

[hrosa]

Please update this guide with latest efforts on RestComm configuration for XMS interop.

http://docs.telestax.com/restcomm-working-with-dialogic-xms/

[gsaslis]

@hrosa i've included some comments in the docker-compose.yml example, included in PR RestComm/Restcomm-Connect#2687 which afaict should cover this scenario?

Could you please take a look here, so we can close this if it does?